1. Field of the Invention
The present invention relates to an electrostatic chuck used to hold semiconductor wafers in the semiconductor manufacturing process.
2. Description of the Prior Art
Hitherto, for the film-forming equipment for affixing film to semiconductor wafers or the etching equipment for carrying out details on semiconductor wafers in manufacturing process of the semiconductor facilities, an electrostatic chuck is used for a jig to hold semiconductor wafers at high accuracy.
For this kind of electrostatic chuck there existed electrostatic chucks comprising an electrostatic electrode 28 embedded inside the ceramic base substrate 22 formed integral with a dielectric layer 23 consisting of ceramics such as alumina, silicon nitride, or aluminum nitride with high insulation capability and a ceramic substrate 24, wherein on the surface of the said dielectric layer 23, grooves 26 were engraved to achieve unevenness, and the top surface of the convex portion 27 was used for a holding surface 25 in order to reduce the area in contact with a semiconductor wafer 100 and to minimize adhesion of foreign matter to the semiconductor wafer 100. Because to form film or carry out etching, it is necessary to uniformly heat the semiconductor wafer 100, the said electrostatic chuck 21 was indirectly heated by a beater or a resistance heating element was embedded in the ceramic substrate 24 composing the electrostatic chuck 21 to directly generate heat.
At the center portion of the said ceramic base substrate 22, a through hole 29 was drilled, and by supplying He and other gas from the said through hole 29 to the groove 26 of the dielectric layer 23, the heat transfer coefficient was increased at the groove portion 26 and the semiconductor wafer 100 sucked and held to the holding surface 25 was designed to be uniformly heated.
However, film forming and etching are carried out under the vacuum condition normally at 1.times.10.sup.-3 torr or lower, but when the semiconductor wafer 100 is electrostatically sucked to the holding surface 25 using the electrostatic chuck 21 as shown in FIG. 3 and He or other gas is supplied to the groove 26 of the holding surface 25, this gas flows out from the clearance between the semiconductor wafer 100 and the holding surface 25 to the inside of the chamber and the vacuum inside the chamber is lost, giving rise to a problem of detrimental effects on the accuracy of film-forming to the semiconductor wafer 100 or processing accuracy.
That is, the excessively small width of the outermost circumference of convex portion 27' in contact with the peripheral portion of the semiconductor wafer 100 generates chipping or cracking at the edge of the convex portion 27' when engraving grooves 26, and as a result even when the semiconductor wafer 100 is sucked and held to the holding surface 25, a clearance is formed between the semiconductor wafer 100 and the convex portion 27', ausing He or other gas to leak.
Even if any chipping or cracking is not generated at the edge of the convex portion 27', excessively rough profile irregularity of the top surface has a possibility to allow He or other gas to leak.
On the other hand, excessively large width of the outermost circumferential convex portion 27' in contact with the peripheral portion of the semiconductor wafer 100 excessively increases temperature difference between inner and outer wall surfaces of the convex portion 27', resulting in poor heat transfer coefficient in the peripheral portion of the semiconductor wafer 100 and impeding heat uniformity, and there is a possibility to cause detrimental effects on film forming accuracy and processing working accuracy.
In addition, the electrostatic chuck 21 shown in FIG. 3 is designed to reduce the area in contact with the semiconductor wafer 100 by engraving grooves 26 on the surface of the dielectric layer 23 in order to reduce the adhesion of foreign matter on the holding surface 25 to the semiconductor wafer 100 to minimum, but excessively shallow groove 26 attracts foreign matter on the bottom surface of the groove 26 to the semiconductor wafer 100 by electrostatic absorption force, giving rise to a problem in that the adhesion of foreign matter is unable to be sufficiently reduced.